Nervous System Development Flashcards
What are the major processes that underlie the formation of the nervous system
- Induction of the neuroectoderm
- regional specialization of the neuroectoderm
- generation of postmitotic, terminally differentiated, diverse neurons and glia
- Migration of newly formed neurons to their final location
- growth of axons, directed by environmental cues, to their targets
- formation of a synapse when a target is reached _
- Numerical matching of the size of the input to the size of the target
- Fine tuning of the final number and location of synapses through competition/experience.
- Myelinzation
When does neuroectoderm start?
at about 18 days post conception and completed by day 26
which does the mesoderm form?
the notochord
which does the ectoderm form?
the neural plate via neuralation
When does the commitment for becoming a certain type of neuron occur?
BEFORE any actual neurons have been formed
Which structure will become the CNS
the neural tube
which structure will become the PNS
the neural crest
Where does the neural tube first close
in the cervical region of the spinal cord
What specific disease can occur if there are defects in neural tube closure
spina bifida
anencephaly
arnold chiari malformation
What are the 3 swellings that form before the neural tube is closed
prosencephalon (forebrain)
mesencephalon (midbrain)
rhombencephalon (hindbrain)
What brain divisions are formed as the process of neuroectoderm specialization continues?
- Telencepahalon (cerebral cortex, basal ganglia, cerebral hemispheres)
- Diencephalon (hypothalamus and thalamus)
- Mesencephalon (midbrain, tectum and tegmentum)
- Metencephalon (pons and cerebellum)
- Myencephalon (medulla
When does post- mitotic, terminally differentiated neurons generation occur
mostly in the 3rd and 4th months of gestation
What factors can negatively impact the process of cell proliferation
maternal use of alcohol
cocaine
other substances
What occurs in the spinal cord and brainstem for generation of post-mitotic differentation?
a. Cells span the width of the tube from the ventricle/central canal to the external surface
b. The nuclei of these cells migrate back and forth between the basal surface and the apical surface
c. Mitosis occurs when the nucleus is at the ventricular surface
d. After mitosis, there are 3 options:
What occurs after mitosis?
Continue the nuclear migration process and continue dividing
ii. Rest
iii. Migrate elsewhere and differentiate into neurons or glia
What occurs in the cerebral cortex for post-mitotic differentiation?
a. During the early stages, the process is similar to that of the spinal cord and brainstem
Cells in the cerebral cortex do retain attachment to which surface?
cortical surface
how is the type of neuron the cells will become determined?
timing at which it makes its last mitotic division dictates what type of neuron it will become
How does migration in the cortex occur?
Radial glial cells guide the migration of neurons to the correct cortical layer. This migrating neuron them attaches to a radial glial fiber and follows it to the cortical surface
What is a growth cone?
transient specialization at the end of a growing axon that navigates the axon to its target by elongating the axon
What kind of factors does the growth cone respond to?
both positive (tropic) and negative
What fibers appear in 3 months
intersegmental fibers
what fibers appear in 5 months
corticospinal fibers
What occurs during the formation of teh synapse stage?
- Presynaptic membrane specialization
- Synthesis and distribution of receptors on the post-synaptic membrane
- Same target receives presynaptic connections from multiple sources therefore receiving far more than it needs
What happens once the axons arrive at the target?
Random initial innervations occurs followed by a fall in the neuronal number
This is due to naturally occurring cell death and synaptic elimination and occurs because of competiton for a limited supply of trophic factors
What are trophic factors
made by postsynaptic cells and are able to activate survival genes
When does fine tuning begin to slow down?
after early adulthood
What is the ongoing competition for synaptic connections dependent on
depends on experiences during critical periods of synaptogenesis
when does myelinization begin?
happens after connections are made and begins in the 4th month but mostly after birth for long tracts
when is myelinzation completed?
completed by age 3
Why are fetal movements important?
• Development of muscles and joints • Role of early reflexes o Muscle/skeletal formation o Assist in preparation for birth and birthing process o Early survival o Provide early movement out of womb
Where does the brain create new neurons during adulthood?
hippocampus and olfactory bulb/tract
